Two projects dealing with the structure and replication of bacterial viruses are continuing. One concerns the restriction of growth of T7 in male strains of E. coli. Our recent work showed that a membrane permeability change occurs early in such infections, resulting in the loss of all the acid-soluble phosphorus-containing pool from the cells. This loss of nucleotides accounts for the cessation of all macromolecular syntheses in such infections. Current work is aimed at determining the cellular and viral functions that lead to the permeability change. The second project extends our observations on the T4 gene 12 product, shown to be the recently seen short tail fibers. Isolated short tail fibers kill E. coli and appear to be responsible for the killing action of T4 ghosts. Current work is focussed on the mechanism by which the fibers kill E. coli. BIBLIOGRAPHIC REFERENCES: J.R. Britton and R. Haselkorn. Permeability lesions in male E. coli infected with bacteriophage T7. Proc. Nat. Acad. Sci. USA 72, 2222-2226 (1975). J.R. Britton and R. Haselkorn. Macromolecular synthesis in T7 infected F' cells. Virology. In the press.